Of course this isn't science, it's just wishful thinking and hand waving about things you don't actually know much about. It's probably worth noting that actual reef scientists aren't so cheerful about the prospects for coral reefs as you are.
It's not even that what you *think* you know is necessarily wrong. You're talking about about something reef scientists aren't particulary worried about: the extinction of coral *species*. In other words it's a straw man. What scientists are worried about is something quite different: a massive reduction in the 348,000 square kilometers of coral reef habitat that currently exist.
That's something that will take millions of years to recover from, and which will cause countless extinctions It will result in multiple species extinctions; sure that's survival of the fittest, but "fittest" doesn't mean "better"; it means more fitted to specific set of new circumstances, in this case circumstances we *chose to create*. And sure, in a few million years it won't matter. But that's not the test we use to decide whether anything other issue needs addressing. If someone broke into your house and took a dump on your kitchen table, it wouldn't matter in a million years, but you'd sure report it to the cops and expect something to get done about it.